Radio Frequency Glow Discharge Research Articles

Deposition of Super‐Hydrophobic and Oleophobic Fluorocarbon Films in Radio Frequency Glow Discharges

AbstractFluorocarbon films using a monomer, 1H, 1H, 2H‐perfluoro–1‐dodecene were deposited in a continuous radio frequency (RF) glow discharge, the process was carried out in a parallel‐plate RF discharge onto stainless steel reactor in order to produce coating with a water‐and oil–repellent surface. Fourier‐Transform Infrared spectroscopy (FT‐IR) and X‐ray Photoelectron Spectroscopy (XPS) revealed that the films obtained contain mainly perfluoromethylene (CF2) species. Film wettability was tested using water and hydrocarbon liquids for contact angle measurements, furthermore surface energy was also calculated. Oil‐repellency was found to increase as the amount of CF2 species increases in the film structure. Film morphology was studied by Atomic Force Microscopy (AFM), films showing an usual morphology from that typical of Plasma Polymerised Fluorocarbon (PPFC) films. The combination of the low surface energy coating and the surface morphology produces materials which are both water and oil repellency.

Simulation of radio-frequency atmospheric pressure glow discharge in γ mode

The existence of two different discharge modes has been verified in an rf (radio-frequency) atmospheric pressure glow discharge (APGD) by Shi [J. Appl. Phys. 97, 023306 (2005)]. In the first mode, referred to as α mode, the discharge current density is relatively low and the bulk plasma electrons acquire the energy due to the sheath expansion. In the second mode, termed γ mode, the discharge current density is relatively high, the secondary electrons emitted by cathode under ion bombardment in the cathode sheath region play an important role in sustaining the discharge. In this paper, a one-dimensional self-consistent fluid model for rf APGDs is used to simulate the discharge mechanisms in the γ mode in helium discharge between two parallel metallic planar electrodes. The results show that as the applied voltage increases, the discharge current becomes greater and the plasma density correspondingly increases, consequentially the discharge transits from the α mode into the γ mode. The high collisionality of the APGD plasma results in significant drop of discharge potential across the sheath region, and the electron Joule heating and the electron collisional energy loss reach their maxima in the region. The validity of the simulation is checked with the available experimental and numerical data.

Development of a Pulsed Radio Frequency Glow Discharge for Three-Dimensional Elemental Surface Imaging. 1. Application to Biopolymer Analysis

Glow discharge optical emission spectrometry has cemented itself as an important surface elemental analysis technique in part because of its superb depth resolution (on the order of single nanometers). However, very few studies have explored the ability of the glow discharge to provide laterally resolved elemental information. In the present study, an end-on-viewed pulsed radio frequency glow discharge is coupled to a monochromatic imaging spectrometer to provide lateral surface imaging. The performance of the technique is demonstrated with etched copper circuits on fiber-glass substrates, and it is shown how several operating parameters including pressure, pulsed mode operation, and time-resolved detection affect the lateral surface resolution. In addition, because a pulsed radio frequency glow discharge offers elemental information on nonconducting samples, the technique is applied to the three-dimensional elemental analysis of proteins on blotting substrates. Several alternative sample types are also examined, including photographic film and glass.

Silane versus silicon tetrafluoride in the growth of microcrystalline silicon films by standard radio frequency glow discharge

Properties of microcrystalline silicon (μc-Si) films produced by standard radio frequency glow discharge from SiH 4 or SiF 4 precursors were studied. Spectroscopic ellipsometry (SE), Raman spectroscopy and time resolved microwave conductivity (TRMC) were used for their characterisation. Although modelling of SE spectra shows that μc-Si films with crystalline fractions up to 100% can be deposited from both types of precursors, we have found that SiF 4 allows obtaining films with improved electronic properties. A detailed analysis of the SE data reveals that such improvement relates to the larger grain size for films deposited from SiF 4 in comparison with the ones deposited from SiH 4. Interestingly, the deposition rate, the fraction of large grains, and the mobility of carriers for the films grown from SiF 4 display close dependencies on the product of pressure and inter-electrode distance. These results are discussed with respect to the contribution of the plasma-synthesised nanocrystals to deposition.

The influence of the depth of a plasma nitrided layer in tool-steel substrate on the scratch-resistant properties of PACVD TiBN coating

A hot-work tool steel was plasma nitrided (PN) to create a diffusion layer beneath the surface. Plasma-assisted chemical vapour deposition (PACVD) was then applied deposit a superhard nano-columnar TiBN coating to the nitrided substrate. The depth of the nitrided diffusion layer was varied to determine its influence on the cohesion and adhesion properties of the coating. Radio frequency glow discharge optical emission spectroscopy (rf-GDOES) revealed multilayers of TiBN and TiN compounds with compositional gradients across the TiBN coating layer. Microhardness measurements (HV 0.025) across the PN diffusion layer in combination with optical microstructure observation showed that an increase in the depth of the nitrided diffusion layer led to an increase in the maximum hardness at the interface between the TiBN coating and the substrate. The maximum hardness correlated linearly with the scratch-resistant properties determined from scratch tests in the progress mode, notably the critical loads corresponding to the first microcracking related to cohesive failure ( L C1), spallation related to adhesive failure ( L C2) and worn out ( L C4). In addition, the scratching coefficients of the TiBN coating on a thicker PN diffusion layer, determined in a scratch test along a scratch track, were all lower than those on a thinner diffusion layer in the substrate. An excessive depth of the nitrided diffusion layer however caused transverse cracking in the substrate. A nitrided layer with an optimum depth can thus improve the adhesion of the PACVD TiBN coating to the tool-steel substrate and the scratch resistance of the coating.

Optical emission spectroscopy of glow discharge plasma from SiH4−CH4 system

AbstractWe used plasma optical emission spectroscopy to investigate the plasma state generated by a radio frequency glow discharge in a monosilane and methane gas mixture. To produce the glow discharge in the gas, we used the source gases separated plasma CVD (SSP‐CVD) method proposed in this research, and the conventional diode method. We studied the flow rate ratio and the radio frequency power dependence of the source gases with the plasma optical emission characteristics generated using these methods, and investigated the relationship between the optical emission states and bond states of the elements in films. We found that the optical emission intensities of SiH and CH radicals in the plasma are related to the carbon content and C‐Si‐H bonds in a‐SiC:H films. Furthermore, we found that more H2 radicals than H radicals exist in plasmas generated by the SSP‐CVD method than in those generated by the conventional method. We used the above results to study the decomposition process of SiH4−CH4 gases. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(2): 9 –16, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ ecjb.20285

Plasma diagnostics and numerical simulations: insight into the heart of analytical glow discharges

This review paper gives an overview of the fundamental studies, both by plasma diagnostics and numerical modelling, that have been carried out for analytical glow discharges. After some introduction about the basic aspects of a glow discharge, the various plasma diagnostic techniques that have been described in the literature for analytical glow discharges will be outlined, including a discussion on their strong and weak points, and a presentation of some characteristic results. The major part of the paper, however, focuses on modelling activities for a better description of glow discharges. An overview is given of possible modelling approaches for glow discharges in general, as a means to point out why we have chosen to describe analytical glow discharges by a hybrid modelling network, consisting of various sub-models. The latter will be briefly described, and typical calculation results will be outlined, mainly for glow discharges in direct current (dc) mode, which are nowadays well described by numerical modelling. The modelling of radiofrequency (rf) glow discharges was found to be more complicated, as described in this review, but we believe that the most important aspects of the rf glow discharge are also correctly predicted. For pulsed discharges, on the other hand, some unanswered questions remain, mainly related to the so-called afterpeak behaviour. Hence, this will need further attention in the future, by modelling and/or plasma diagnostic measurements.

Non-fouling microfluidic chip produced by radio frequency tetraglyme plasma deposition

This Technical Note presents the direct surface modification of a glass/PTFE hybrid microfluidic chip, via radio frequency glow discharge plasma polymerisation of tetraethlylene glycol dimethylether (tetraglyme), to produce hydrophilic, non-fouling, PEO-like surfaces. We use several techniques including X-ray photoelectron spectroscopy (XPS), direct enzyme-linked immunosorbent assays (ELISA) and immunofluorescent imaging to investigate the channel coatings. Our results indicate the successful deposition of a PEO-like coating onto microchannel surfaces that has both solution and shelf stability (>3 months) and is capable of preventing fibrinogen adsorption to the microchannel surfaces.

A method for characterizing adsorption of flowing solutes to microfluidic device surfaces

We present a method for characterizing the adsorption of solutes in microfluidic devices that is sensitive to both long-lived and transient adsorption and can be applied to a variety of realistic device materials, designs, fabrication methods, and operational parameters. We have characterized the adsorption of two highly adsorbing molecules (FITC-labeled bovine serum albumin (BSA) and rhodamine B) and compared these results to two low adsorbing species of similar molecular weights (FITC-labeled dextran and fluorescein). We have also validated our method by demonstrating that two well-known non-fouling strategies [deposition of the polyethylene oxide (PEO)-like surface coating created by radio-frequency glow discharge plasma deposition (RF-GDPD) of tetraethylene glycol dimethyl ether (tetraglyme, CH(3)O(CH(2)CH(2)O)(4)CH(3)), and blocking with unlabeled BSA] eliminate the characteristic BSA adsorption behavior observed otherwise.

Rf glow discharge optical emission spectrometry for cleaning process control of oil residues in low alloy steel

Radiofrequency glow discharge optical emission spectrometry (rf-GD-OES) has been investigated as an assessment tool in the control of cleaning processes developed to remove oil residues covering the surface of the steel. The control of the cleaning process has a special importance on the production of zinc and zinc alloy coatings on steel as a corrosion protection. One of the most important methods used in producing zinc coatings is the immersion of steel in a liquid bath of zinc or a zinc alloy. Therefore, prior to this immersion, the cleaning of oil residues remaining on the steel sheet from previous processing steps is of great importance. Two cleaning processes have been investigated. Qualitative and quantitative rf-GD-OES results have been used to control the carbon-based impurities present on the surface of the steel sheet.

Surface characterization of plasma deposited nano-structured fluorocarbon coatings for promoting in vitro cell growth

Nano-structured “teflon-like” coatings characterized by highly-fluorinated, random, ribbon-shaped, micrometers-long structures were deposited on polyethylenetherephtalate (PET) substrates by plasma enhanced-chemical vapour deposition (PE-CVD) using modulated radiofrequency (RF, 13.56 MHz) glow discharges fed with C 2F 4 in modulated discharge (MD) and continuous wave (CW) regimes. Surfaces obtained in this way featured identical chemical composition and different roughness in the nanometric scale. Water contact angle (WCA) measurements, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were utilized to characterize the surfaces. A positive relationship was shown to exist between the WCA value and the mean nano-structure height and the area root-mean-square (RMS) roughness of coatings. The possibility of obtaining coatings of varying nano-structure height, i.e., roughness, in a nanometric scale represents a promising result for further use of these surfaces as substrates for experiments on cell adhesion, proliferation and growth.

PARALLELIZING AN APPLICATION WITH TIME-INCREASING WORKLOAD USING ADAPTIVE PROCESSOR ALLOCATION

This paper presents our experience in parallelizing a Monte Carlo/fluid hybrid simulation of radio frequency glow discharge in plasma physics. The application is a dynamic loosely-synchronous system with time-increasing workload. We adopt adaptive processor allocation to effectively parallelize the time-increasing workload. The results show that adaptive processor allocation has potential to improve performance of parallel applications with time-varying workloads. The methods proposed in this paper can be applied to other dynamic loosely-synchronous applications as well.

Discharge characteristics of atmospheric-pressure radio-frequency glow discharges with argon/nitrogen

In this letter, atmospheric-pressure glow discharges in γ mode with argon/nitrogen as the plasma-forming gas using water-cooled, bare copper electrodes driven by radio-frequency power supply at 13.56MHz are achieved. The preliminary studies on the discharge characteristics show that, induced by the α-γ coexisting mode or γ mode discharge of argon, argon-nitrogen mixture with any mixing ratios, even pure nitrogen, can be employed to generate the stable γ mode radio-frequency, atmospheric-pressure glow discharges and the discharge voltage rises with increasing the fraction of nitrogen in the argon-nitrogen mixture for a constant total gas flow rate.

Modulating bone cells response onto starch-based biomaterials by surface plasma treatment and protein adsorption

The effect of oxygen-based radio frequency glow discharge (rfGD) on the surface of different starch-based biomaterials (SBB) and the influence of proteins adsorption on modulating bone-cells behavior was studied. Bovine serum albumin, fibronectin and vitronectin were used in single and complex protein systems. RfGD-treated surfaces showed to increase in hydrophilicity and surface energy when compared to non-modified SBB. Biodegradable polymeric blends of cornstarch with cellulose acetate (SCA; 50/50wt%), ethylene vinyl alcohol (SEVA-C; 50/50wt%) and polycaprolactone (SPCL; 30/70wt%) were studied. SCA and SCA reinforced with 10% hydroxyapatite (HA) showed the highest degree of modification as result of the rfGD treatment. Protein and control solutions were used to incubate with the characterized SBB and, following this, MG63 osteoblast-like osteosarcoma cells were seeded over the surfaces. Cell adhesion and proliferation onto SCA was found to be enhanced for non-treated surfaces and on SCA+10%HA no alteration was brought up by the plasma modification. Onto SCA surfaces, BSA, FN and VN single solutions improved cell adhesion, and this same effect was found upscaled for ternary systems. In addition, plasma treated SEVA-C directed an increase in both adhesion and proliferation comparing to non-treated surfaces. Even though adhesion onto treated and untreated SPCL was quite similar, plasma modification clearly promoted MG63 cells proliferation. Regarding MG63 cells morphology it was shown that onto SEVA-C surfaces the variation of cell shape was primarily defined by the protein system, while onto SPCL it was mainly affected by the plasma treatment.

Glow discharge modified tissue culture polystyrene: role of surface chemistry in cellular attachment and proliferation

A radio frequency glow discharge has been used to selectively deposit non-polar hydrocarbon films onto tissue culture grade polystyrene surfaces. The resulting surfaces have been studied using X-ray photoelectron spectroscopy, contact angle analysis and atomic force microscopy. Regions with differing surface chemistry and polarity have been produced on the same substrate using a simple masking technique and allowed the spatially controlled attachment of mammalian cells. The attachment of cells to plasma modified tissue culture polystyrene surfaces has been correlated to the concentration of specific oxygen functional groups.

Spatial distribution of SiCl n ( n =0–2) in SiCl 4 plasma measured by mass spectroscopy

For a better understanding of the deposition mechanism of thin films in SiCl4 source gas, we have measured the spatial distributions of SiCln (n=0–2) radicals in SiCl4 radio frequency glow discharge plasma utilizing a mass spectrometer equipped with a movable gas sampling apparatus. The experimental results demonstrate that the relative densities of SiCln (n=0–2) radicals have peak values at the position of 10 mm above the powered electrode along the axial direction; the relative densities of the Si and SiCln (n=1, 2) radicals have peak values at the positions of 27 mm and 7 mm away from the axis along the radial direction, respectively. Generally speaking, in the whole SiCl4 plasma bulk region, the relative density of Si is one order of magnitude higher than that of SiCl, and the relative density of SiCl is several times higher than that of SiCl2. This reveals that Si and SiCl may be the primary growth precursors in forming thin films.

Glow discharge plasma treatment of polyethylene tubing with tetraglyme results in ultralow fibrinogen adsorption and greatly reduced platelet adhesion

Previous studies from our lab have shown that fibrinogen adsorption (Gamma(Fg)) must be reduced below 10 ng/cm(2) to significantly reduce platelet adhesion, and that radio frequency glow discharge (RFGD) treatment of polymeric films in the presence of tetraethylene glycol dimethyl ether (tetraglyme) can reduce Gamma(Fg) to the desired ultralow value. In this report, the effects of RFGD coatings of tetraglyme on the lumenal surface of PE tubing on Gamma(Fg) and on blood interactions both in vitro and ex vivo are described. Gamma(Fg) on the tetraglyme-coated PE tubing was reduced to the desired ultralow level (<10 ng/cm(2)), and we also observed a significant decrease in adsorption of von Willebrand's factor. In vitro platelet adhesion from washed platelet suspensions, platelet rich plasma, or whole blood to tetraglyme-coated PE tubing was decreased compared to PE, polyurethane, or silicone rubber tubes. In addition, thrombin generation by platelets adherent to tetraglyme-coated PE was also much less than by platelets adherent to PE. When inserted in an ex vivo carotid artery-carotid artery shunt in sheep, the RFGD tetraglyme-coated PE exhibited a very low number of adherent platelets compared to heparin-coated, chromic acid-etched, or plain PE. The RFGD tetraglyme-coated PE tubes exhibited high protein and platelet resistance in vitro, and high platelet resistance ex vivo. The improved hemocompatibility is attributed to the unique chemical structure of RFGD tetraglyme that makes it highly protein resistant.

A comparative study between inductively and capacitively coupled plasma deposited polystyrene films: chemical and morphological characterizations

Thin polystyrene films were deposited on stainless steel substrates by capacitively and inductively coupled radio frequency glow discharge plasma, in order to compare their chemical and morphological properties. The films were characterized by Fourier-transform infra red spectroscopy (FTIR), X-Ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), atomic force microscopy (AFM) and scanning electron microscope (SEM). Wettability properties were also determined by contact angle measurements. Ageing effect was studied by analysing films aged for 15 min and for 1 week. Results from both capacitively and inductively plasma polymerized polystyrene (pPS) films aged for 15 min showed that the chemical structure of the bulk, chemical composition of the surface (depth < 10 nm) and wettability properties were rather similar. Only their microstructures were very different: the pPS(capa) film's microstructure showed homogeneous distribution of spherical particles of about 100 nm in diameter but the pPS(ind) film's microstructure seemed to be mainly influenced by the surface of the metallic substrate: orientated 'lamellae-like layers' of polymers were observed on each metallic grain. Ageing for 1 week in ambient air induced low oxygen uptake in the surface of both pPS films. The pPS(ind) topmost surface (depth < 3 nm) was more oxidized than that of pPS(capa) but no modification of the chemical structure of the bulk or of the morphology was noticed after ageing. Copyright (C) 2006 John Wiley & Sons, Ltd.

Influence of surface pre-treatments on disturbed rolled-in subsurface layers of aluminium alloys

Rolling is known to alter the surface properties of aluminium alloys and to introduce disturbed subsurface layers. These layers are characterised by a refined grain structure, rolled-in oxide particles, a fine distribution of intermetallic particles, various voids and cracks.In this study, the effects of some surface pre-treatments, i.e., alkaline etching at various temperatures and chemical cleaning with Nabuclean and CrO3/H3PO4, on these rolled-in layers are investigated by means of surface analytical techniques. The changes in composition and morphology of the (sub)surface are studied with scanning electron microscopy/energy dispersive X-ray analysis and backscattered electron imaging (SEM/EDX+BEI). The presence of incorporated oxide particles is evaluated by measuring the total reflectance. The (re-)distribution of alloying, impurity and trace elements upon these surface treatments is investigated with radiofrequency glow discharge optical emission spectrometry (rf-GDOES).

A New Generation of Catalytic Poly(vinylidene fluoride) Membranes: Coupling Plasma Treatment with Chemical Immobilization of Tungsten‐Based Catalysts

AbstractA new generation of catalytically active membranes for secondary amine oxidation and phenol degradation has been developed by coupling the advantages of low‐temperature plasma‐modification processes with surface chemical immobilization reactions of catalysts. Poly(vinylidene fluoride) membranes have been modified with NH3 radiofrequency glow discharges in order to graft amino groups at their surface, providing active sites for stable immobilization of tungsten‐based heterogeneous catalysts. Particular attention has been focused on tungstate, WO42–, and decatungstate, W10O324–, which act efficiently as catalysts for the oxidation of secondary amines and as photocatalysts for the degradation of organic pollutants, respectively. Plasma‐modified membranes surface‐tailored with WO42– have been used in catalytic membrane reactors to activate hydrogen peroxide for oxidizing secondary amines to nitrones; membranes modified with W10O324– have been used for the complete degradation of phenol. The obtained results, in terms of amine–nitrone conversion and phenol degradation, respectively, appear extremely promising; these modified membranes can be considered as a pioneering, successful example of heterogenization of W‐based catalysts on plasma‐treated membranes.